Magnetic bodies having magnetic anisotropy comprising conjoined thin films of molybdenum and nickel coated on a non-conductive substrate



March 29, 1966 J LOMMEL ETAL 3,243,269

MAGNETIC BODIES HAVING MAGNETIC ANISOTROPY COMPRISING CONJOINED THIN FILMS OF MOLYBDENUM AND NICKEL COATED ON A NON-CONDUCTIVE SUBSTRATE Filed Feb. 28, 1962 2 (mensuex/va FIELD I000oe TOR UE fees/cw ZOFF/LM ANGLE 0F FIELD Fl/ I fr) veno r-s: James M. Lemmeh Char/es 1262-19 277 dn;

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United States Patent MAGNETIC BODIES HAVING MAGNETIC ANISOT- ROPY COMPRISING CONJOINED THIN FILMS 0F MOLYBDENUM AND NICKEL COATED ON A NON-CONDUCTIVE SUBSTRATE James M. Lornmel and Charles D. Graham, Jr., Schenectady, N.Y., assignors to General Electric Company, a corporation of New York Filed Feb. 28, 1962, Ser. No. 176,319 3 Claims. (Cl. 29-183.5)

This invention relates to magnetic bodies and more particularly to magnetic bodies having improved residual to saturation induction ratios, uniaxial magnetic anisotropy and to a process for producing such bodies.

It is an object of this invention to provide th1n film magnetic bodies having rotatable, uniaxial, magnetic anisotropy.

An additional object of this invention is to provide thin film magnetic bodies having improved residual to saturation induction ratios.

A further object of this invention is to provide a process for producing a metallic thin film body having rotatable, uniaxial, magnetic anisotropy and an improved residual to saturation induction ratio.

Other objects and advantages of this invention will be in part obvious and in part explained in reference to the accompanying specification and drawings.

In the drawings, FIGURE 1 shows magnetic torque curves obtained whenthe bodies of this invention were rotated in applied magnetic fields. FIGURE 2 shows a cross-section through a body produced according to this invention.

Broadly, the metallic bodies of this invention comprise metallic laminates including conjoining thin film layers of molybdenum and nickel, these bodies having uniaxial, magnetic anisotropy in which the easy direction of magnetization can be readily changed by application of a magnetic field in excess of that field used for measuring the uniaxial anisotropy. Rotatable anisotropy here refers to the ability to rotate the easy axis of magnetization by use solely of applied magnetic fields.

The process is one wherein a suitable substrate body constructed of some non-conductive material, such as glass, is covered with a thin film of molybdenum, the molybdenum being deposited by evaporating molybdenum from a heated wire in a vacuum environment, and the thus coated substrate then exposed to air. The molybdenum film is heated to an elevated temperature, generally not less than about 300 C., in a vacuum to assure removal of any adsorbed water which may have been formed thereon during its exposure to air. Following this baking-out operation, a thin film of nickel is vapor deposited on to the molybdenum film by subjecting the molybdenum to nickel vapor in a vacuum environment. The laminated film structure formed has the molybdenum and nickel films in conjoining relationship and possesses rotatable, uniaxial, magnetic anisotropy.

This invent-ion, as already mentioned, is concerned with bodies possessing rotatable, magnetic anisotropy and to methods for producing such bodies. It has long been recognized that magnetic bodies can be produced in which preferred directions of magnetization exist. However, even with the application of excessively large magnetic fields to these bodies, these preferred directions of magnetization cannot be changed. The production of bodies possessing rotatable, uniaxial, magnetic anisotropy of the type wit-h which the present invention is concerned has been possible in certain metal-metal oxide composites but not in combinations of the type herein described. For example, see the copending application of W. H. Meiklejohn, Serial No. 149,000, filed Oct. 31, 1961, and now 3,243,269 Patented Mar. 29, 1966 Patent No. 3,116,255 and assigned to the same assignee as the present invention.

Considering the present process in more detail, the preferred practice is to provide a suitable substrate body 15, such as glass, which supports the metallic laminate. The use of such a substrate is desirable, since the total thickness of the thin film, nickel-molybdenum laminate does not exceed 5000 A. and is therefore not self-supportmg.

The substrate body is subjected to a vacuum of not less than about 10 mm. of Hg at an elevated temperature, i.e., not less than about 300 C., to effect removal of any adsorbed contaminants which may be present on its exposed surfaces. Following this operation, the body is placed within an evacuated chamber in the presence of a molybdenum wire which is resistance heated to a temperature sufficient to vaporize the wire and deposit a molybdenum film 16 on the substrate.

The next step in the operation is that of removing the molybdenum covered substrate from the evacuated chamber and subjecting it to air. The time of contact wit-h air does not appear important, although the act of making such contact is felt essential to obtain-ment of the desired magnetic properties.

Once the molybdenum covered substrate has been exnickel can be deposited by different methods involving the vapor transport of the nickel. For example, molten nickel may be placed within a suitable receptacle in a vacuum chamber containing the molybdenum covered substrate body so that a partial pressure of nickel is present in the atmosphere of the vacuum chamber for deposition onto the molybdenum film. Deposition of nickel is conducted only for a time sufficient to deposit a film of nickel having a thickness not less than about A. and when this time has elapsed, the body is removed from the vacuum chamber and is ready for application.

As a specific example of a body produced according to this invention, glass substrates were first baked at temperatures approximating 400 C. in a vacuum of 10- mm. Hg. The bodies were then coated with molybdenum deposited from a hot molybdenum wire in a vacuum of 10- mm. Hg and then exposed to air. All of the specimens were baked at 400 C. at pressures of 10* mm. Hg and nickel deposited thereon from a molten source held in an Alundum crucible at pressure of 10* and 10 mm. Hg.

The .bodies produced as outlined above, comprised a laminated film structure consisting of conjoining films of nickel and molybdenum, these being the materials felt responsible for the presence of the rotatable, uniaxial magnetic anisotropy. These bodies were measured in a torque magnetometer and it was found that in fields on the order of 750 oersteds large magnetic anisotropy was netic anisotropy in the plane of the film. The torque in the body was measured in an applied magnetic field of 1000 oersteds both before and after the easy direction of magnetization was changed by the application of an applied magnetic field of about 2500 oersteds. Curves and 11 indicate that the easy direction of magnetization has been changed from point A to point B by the use of a field of 2500 oersteds applied at about 90 to the original direction.

Although the present invention has been described in connection with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An article of manufacture having rotatable magnetic anisotropy comprising, an electrically nonconductive substrate body, a thin'film of molybdenum on said substrate, and a film of nickel not less than about 100 A. in thickness conjoining said molybdenum film, the total combined thickness of said nickel and molybdenum films being not greater than about 5000 A.

2. An article of manufacture having rotatable magnetic anisotropy and being characterized in that the magnitude of the magnetic field necessary to alfect rotation of the easy axis of magnetization is sufiiciently in excess of 1,000 .oersteds comprising, an electrically nonconductive substrate body, a thin film of molybdenum on said substrate, and film of nickel not less than about 100 A. in thickness conjoining said molybdenum film, the total combined thickness of said nickel and molybdenum films being not greater than about 5,000 A.

3. An article of manufacture having rotatable magnetic anisotropy and being characterized in that the magnitude of the magnetic field necessary to affect rotation of the easy axis of magnetization is at least 2,500 oersteds comprising, an electrically nonconductive body, a thin film of molybdenum of said substrate, and a film of nickel not less than about A. in thickness conjoining said molybdenum film, the total combined thickness of said nickel and molybdenum films being not greater than about 5,000 A.

References Cited by the Examiner UNITED STATES PATENTS 2,185,300 1/1940 Hickman.

2,519,728 8/1950 Alexander 117 107 2,619,432 11/1952 Hosmer 117 71 2,628,927 2/1953 Colbert et al 117 71 X 2,667,427 1/1954 Nolte 117 71 X 2,701,849 2/1955 Penning et a1. 117 107 X 2,900,282 8/1959 Rubens 117 107 X 3,066,236 11/1962 Sandbank 117-217 3,102,048 8/1963 Gran et al. 340- -174 OTHER REFERENCES Graham et al.: Magnetic Anisotropies of Nickel Films Evaporated and Measured at 10- mm. Hg and Below, Journal of Applied Physics, supplement to vol. 32, No. 3, March 1961, pp. 83S and 84S, QC-1-J-82.

Holland, Vacuum Deposition of Thin Films, John Wiley and Sons, Inc., New York, 1956, pp. 30, 31, 74, and 75, TS-695-H6 c.2.

Williams et al.: Magnetic Domain Patterns on Thin Films, Journal of Applied Physics, vol. 28, No. 5, May 1957, pp. 548-555 (pp. 554 and 555 relied on), QC-l- J-82.

Smith: Magnetization Reversal and Thin Films, Journal of Applied Physics, vol. 29, No. 3, March 1958, pp. 264-273 (pp. 264 and 265 relied on).

RICHARD D. NEVIUS, Primary Examiner. P. H. KONDO, R. B. MURRAY, Assistant Examiners. 

1. AN ARTICLE OF MANUFACTURE HAVING ROTATABLE MAGNETIC ANISTROPY COMPRISING, AN ELECTRICALLY NONCONDUCTIVE SUBSTRATE BODY, A THIN FILM OF MOLYBDENUM ON SAID SUBSTRATE, AND A FILM OF NICKEL NOT LESS THAN ABOUT 100 A. IN THICKNESS CONJOINING SAID MOLYBDENUM FILM, THE TOTAL COMBINED THICKNESS OF SAID NICKEL AND MOLYBDENUM FILMS BEING NOT GREATER THAN ABOUT 5000 A. 